1. Field of the Invention
The present invention relates to a multilayer wiring device and an insulator film thereof.
2. Description of the Related Art
A drop in the signal propagation speed by the increase of parasitic capacity of an insulator film for a semiconductor device has been known, but the line delay did not have a major influence on an entire device at the generation in which the line space of a semiconductor device exceeded 1 μm. But the influence on the device speed becomes major when the line space is 1 μm or less, and in particular the influence of the parasitic capacity between the lines on the device speed will be significant if circuits are formed with a 0.1 μm or less line space in the future.
Specifically, as the degree of integration of semiconductor integrated circuits increases and device density improves, the demand for multilayer semiconductor elements is increasing, particularly. In this trend, the line space is becoming smaller, for example, due to the higher degree of integration, and the line delay caused by the increase of capacity between lines is becoming a problem. The line delay (T) is influenced by the line resistance (R) and the capacity between lines (C), and is given by the following Formula 1.T∝CR  (1)
In Formula 1, the relationship of ∈ (dielectric constant) and C is shown in Formula 2.C=∈0∈rS/d  (2)(where S is an electrode area, ∈0 is the dielectric constant of a vacuum, ∈r is the dielectric constant of an insulator film, and d is a line space.) Therefore in order to decrease the line delay, decreasing the dielectric constant of an insulator film is effective.
Currently, low-dielectric-constant coating-type insulator films, etching stopper layers formed by plasma CVD, and diffusion-barrier insulator films are mainly used as insulator films in the multilayer wiring structures of multilayer wiring devices such as semiconductor devices.
Traditionally, films of inorganic materials such as silicon dioxide (SiO2), silicon nitride (SiN), phosphorus silicon glass (PSG), etc., or organic polymers such as polyimides have been used for these insulators. However, CVD-SiO2 films most frequently used for semiconductor devices have a specific dielectric constant as high as about 4. Although SiOF films which have been investigated as a low-dielectric-constant CVD film show a specific dielectric constant of about 3.3-3.5, they are highly hygroscopic, resulting in increase of the dielectric constant. In addition, in recent years, as low-dielectric-constant films, porous coatings are becoming known which are obtained by addition of organic resins or the like that are evaporated or decomposed by heating, into materials for low-dielectric-constant films, followed by heating during the film forming to make them porous. However, they have poor mechanical strength generally due to the porosity. Because the current pore size is as large as not less than 10 nm, if the porosity is increased so as to decrease the dielectric constant, the increase of dielectric constant due to moisture absorption as well as decrease of film strength tend to occur.
To solve these problems, processes have been investigated in which an insulator film after film formation is cured by ultraviolet rays, plasma beams or electron beams in order to provide the film with a higher strength. However, increase of dielectric constant and film thickness thinning of the insulator films due to elimination of organic groups (mainly CH3 group) tend to occur in any of the processes, providing insufficient results. Processes have been also investigated in which a high-density insulator film is formed on a porous insulator film, over which ultraviolet rays, plasma beams or electron beams are irradiated as a trial to suppress such damage and increase the film strength while maintaining a low dielectric constant (References 1 and 2).                Reference 1: Japanese Patent Application 2004-356618 (claims)        Reference 2: Japanese Patent Application 2005-235850 (claims)        